Nest building and circulating testosterone dynamics in male zebra finches, Taeniopygia guttata

Despite its fundamental importance for avian reproduction, the hormonal mechanisms supporting nest building remain poorly understood. While nest building by both male and female builders requires circulating sex steroids, it is not clear whether these steroids are required throughout building. We, therefore, sought to determine circulating testosterone dynamics in male zebra finches during early breeding, specifically focusing on the nest building period. We collected plasma samples from two cohorts of birds at three of the following four timepoints: before (baseline), following pairing, during, and after nest building. To dissociate the end of nest building from incubation onset we daily removed any eggs laid and terminated nest building once we had sampled males during nest building. Male circulating testosterone levels remained stable following pairing with a female and throughout nest building. However, testosterone titers dropped once nest building had stopped. We also found evidence to suggest that, following pairing with a female, circulating testosterone titers can predict a male's future readiness to build. Together, our data suggest that circulating testosterone is important throughout nest building, not decreasing until the end of nest building activities, perhaps through a 'self-feedback' mechanism.